The invention relates to a disc brake for a commercial vehicle.
In a disc brake, which is known from DE 94 22 342 U1, a rotary lever acts on a bridge which is positioned in a brake caliper and in which two adjusting spindles are mounted. Each adjusting spindle includes a pressure piece for receiving a brake pad. The brake pad consists of a pad carrier plate and a friction pad fastened thereto. The brake pad is pressed onto a brake disc in the case of a braking operation. The two adjusting spindles are provided with an external thread and are screwed in each case into a respective threaded bore of the bridge.
By way of a wear adjusting device which is assigned to one of the adjusting spindles, the brake pad is applied, as a result of rotation of the adjusting spindles in the threaded bores, in the case of wear of the friction pad, such that an air gap between the brake pad and the brake disc always remains substantially constant. To this end, an adjuster which is arranged concentrically in one of the adjusting spindles is driven via a drive element by the rotary lever.
Since, however, the adjuster is positioned merely in one adjusting spindle, but the adjustment of the brake pad is to take place uniformly and the second adjusting spindle therefore also has to be adjusted correspondingly, a preferably positively locking traction mechanism drive is provided, which transmits the rotational movement of one adjusting spindle to the other synchronously. For example, a link chain which is guided in a circulating manner on chain sprockets of the adjusting spindles is used as traction mechanism. The use of a toothed belt which is then in engagement with gearwheels is also known.
However, the known constructions all have the disadvantage that the traction mechanism drive, that is to say the synchronizing device, is arranged outside the brake caliper, a closure cover which covers the synchronizing device usually being provided, in order to both protect the synchronizing device against weather influences and to seal passage openings in the brake caliper toward the adjusting spindles.
In order to fasten it, but also in order to seal it with respect to the brake caliper, relatively complicated measures are required, which can be realized only with correspondingly expensive production steps.
Moreover, the synchronizing device and the closure cover which covers it add height to the brake caliper and therefore conflict with the constant requirement for minimization of the overall brake dimensions.
The invention is based on the object of developing a disc brake of the above-described type such that it can be produced more simply and less expensively, and its dimensions are minimized.
This and other objects are achieved by way of a disc brake having a brake caliper which engages over a brake disc, a brake application device which is arranged in the brake caliper for pressing brake pads onto the brake disc, two adjusting spindles which are arranged parallel to one another and at a spacing from one another and are mounted rotatably by way of a corresponding thread in a bridge, on which a rotary lever of the brake application device acts, a wear adjusting device which is positioned in the brake caliper and by way of which a wear-induced change in an air gap between the brake pad and the brake disc can be compensated for substantially via an axial adjustment of the adjusting spindles, and a synchronizing device with a traction mechanism drive, by way of which the two adjusting spindles can be adjusted synchronously. The fraction mechanism drive has a traction mechanism which acts in a force-transmitting manner on drive wheels which are in operative connection with the adjusting spindles such that they cannot rotate. Each drive wheel has at least one positively locking element, which acts on an outer-side axial guide of the associated adjusting spindle.
The possibility of extraordinarily space-saving accommodation is provided by way of the configuration according to the invention of the adjusting or synchronizing device. This permits an arrangement of the synchronizing device inside the brake caliper. The arrangement suitably takes place on that side of the bridge which faces the brake pad, since the rotary lever bears against the bridge on the opposite side.
Otherwise, the adjusting spindles protrude out of the bridge in the direction of the brake pad, that is to say in the direction of the connected pressure pieces, as a result of which sufficient space remains for positioning the drive wheels which are mounted rotatably on integrally formed attachments of the bridge.
As a result of the accommodation of the synchronizing device inside the brake caliper, the brake caliper and/or the disc brake is not only more compact overall, but the use of an external closure cover can also be dispensed with, as well as previously necessary sealing measures in the brake caliper with respect to the closure cover.
In this way, cost savings which are certainly notable, can naturally be achieved which, above all, are also significant because disc brakes are produced as serial parts in large numbers.
In addition to the purely structural advantages, which also include the fact that a potentiometer which is necessary for wear detection can be arranged inside the brake caliper, functional advantages are also achieved. These include, in particular, the possibility of already carrying out the synchronization of the two adjusting spindles before complete assembly of the brake.
To this end, each drive wheel is configured in two pieces, consisting of an outer wheel, into which the traction mechanism engages, and an inner wheel. The outer wheel and inner wheel are held with respect to one another such that they cannot rotate by way of a toothing system which engages into one another.
Whereas the outer wheel has an external toothing system with a relatively coarse tooth spacing for the positively locking connection to the traction mechanism, for example a link chain or a toothed belt, the tooth spacing of the corresponding outer wheel/inner wheel toothing system is kept fine, that is to say small, with the result that very accurate presetting of the adjusting spindles is possible.
The at least one positively locking element according to the invention, by way of which the respective drive wheel is held on the associated adjusting spindle such that it cannot rotate, but is displaceable axially, can consist of a ball, a feather key or a comparable component which is held in the drive wheel. The positively locking element is guided on an outer-side axial guide, preferably in an axial groove or on a guide face of the adjusting spindle. A ball is highly suitable, in particular, because it acts in a low-friction manner during the adjustment of the adjusting spindle.
Each adjusting spindle preferably has a plurality of axial guides which are preferably arranged at an identical angular spacing from one another and on which in each case at least one positively locking element is guided.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.